This invention relates to air conditioners, and more particularly to a control circuit for an air conditioner in which signal lines are connected between its indoor and outdoor units for controlling the operation of the air conditioner.
In an air conditioner of separate type in which an outdoor unit containing an air compressor, a blower, a four-way selector valve, an outdoor heat exchanger, etc. therein is disposed separately from an indoor unit containing a blower, an expansion valve, an indoor heat exchanger, etc., power is supplied from an AC three-phase power source common to the indoor and outdoor units, and lines connected to an actuating circuit are led out from two phases of the AC three-phase power source. When the AC three-phase power source is a high-voltage one, the voltage is transformed into a low voltage by a transformer, while when it is a low-voltage one, the voltage is supplied intact to actuate the individual components. Accordingly, one of the lines led out from the two phases functions as a common line, and an electromagnetic contactor for compressor operation, electromagnetic contactors for blower operation, four-way selector valve, various solenoid valves, etc. are connected to the other line. These contactors and valves must be connected in parallel to prevent voltage drops across their coils.
In order to operate the individual components of the indoor and outdoor units by application of signals, a signal line transmitting a signal commanding the operation of the compressor and another signal line transmitting a control signal controlling the four-way selector valve are required for signal transmission from the indoor unit to the outdoor unit, and also a signal line transmitting a signal indicative of operation of a protective equipment such as a sensor sensing an overcurrent of the compressor and another signal line transmitting a signal indicative of defrosting operation of a deicer are required for signal transmission from the outdoor unit to the indoor unit.
In a transmission circuit transmitting such voltage signals, each of the signals occupies one signal line, and a common line is additionally required. This means that the number of signal lines increases in proportion to the number of signals. Therefore, such a signal transmission circuit has been defective in that material and construction costs increase inevitably, and yet the probability of misconnections during wiring is still high.
With a view to obviate the above defect and in an attempt to decrease the number of signal transmission lines between the indoor and outdoor units, Japanese Utility Model Publication No. 55-31476 (1980) and Japanese Patent application Laid-open No. 55-20305 (1980) were proposed.
In the former or Japanese UM Publication No. 55-31476, a semiconductor deicer is divided into an indoor part and an outdoor part which are connected by a DC signal line, and a significant signal whose significance depends on its output level is transmitted over this signal line. Therefore, a complex device is required for the transmission and reception of the significant signal.
In the latter or Japanese Patent Application Laid-open No. 55-20305, an air conditioner is divided into an indoor unit and an outdoor unit which are connected by two DC signal lines, and a significant signal in the form of a pulse signal is transmitted over the signal lines. Therefore, in this case too, a complex device is required for the transmission and reception of the significant signal, as in the former case.